where would you be making the split? as far as performance goes, there's not really a point, but if you split the exhaust too close to the engine you will lose back pressure and low-end torque...
I think it's purely cosmetic on an inline engine. But if you must do it, I think the best way to accomplish this is to use a single muffler pan, with one input and two output pipes. Mount the muffler transversely under the trunk and have the output pipes exit on either side. That's how I did mine and it works beautifully.